AGING AND THE LIFE COURSEcomponent of age stratification allocates roles and
resources and assigns differential social value to
age strata. Thus, ageism is largely an effect of age
stratification. On the other hand, by promoting
age consciousness, age stratification sets the stage
for age-based public policies and collective efforts
by older adults to protect or increase their share of
societal resources (e.g., voting and lobbying ef-
forts based on the self-interests of the elderly).
In the 1990s, the sociology of aging focused on
change and stability across the life course. Life-
course perspectives have enriched aging research
in several ways (e.g., Elder 1995; George 1993).
First, a life-course approach is attractive because it
recognizes that the past is prologue to the future.
That is, status and personal well-being in late life
depend in large part on events and achievements
experienced earlier in the life course. Second, life-
course perspectives emphasize relationships across
life domains, recognizing that, for example, family
events affect and are affected by work and health.
Traditionally, sociological research has focused on
specific life domains (e.g., the sociology of work,
the sociology of the family); life-course perspec-
tives, in contrast, are person-centered rather than
domain-centered. Third, life-course perspectives
focus on the intersection of history and personal
biography. Although the macro-micro schism re-
mains difficult to bridge, life-course research has
documented some of the complex ways that his-
torical conditions affect personal lives both
contemporaneously and over subsequent decades.
THE AGE-PERIOD-COHORT PROBLEMIsolating the effects of age and characterizing the
aging process are difficult tasks. Because many
factors affect social structure and individual be-
havior, it is always difficult to isolate the effects of a
specific factor. But this task is especially difficult
with regard to age, because it is inherently con-
founded with the effects of two other factors:
cohort and period. Age, of course, refers to time
since birth, and age effects refers to patterns result-
ing from the passage of time or sheer length of life.
Cohort refers to the group of persons born at
approximately the same time (e.g., the 1920 co-
hort, the 1940–1944 cohort). There are two prima-
ry kinds of cohort effects. One type results from
historical factors. For example, cohorts who lived
through the Great Depression or World War II
had different life experiences than cohorts who
were not exposed to those historical events. And,
as a further complication, the effects of historical
events vary depending on the ages of those who
experience them. The second type of cohort effect
reflects compositional characteristics. For exam-
ple, large cohorts (such as the Baby Boomers) may
face greater competition for social resources than
smaller cohorts (e.g., those born during the Great
Depression, when fertility rates were low). Both
types of cohort effects can have persistent effects
on the life course, and, hence, late life. Period effects
(also called time of measurement effects) result from
events or situations that happen at a specific time,
and tend to affect individuals regardless of age or
cohort. For example, faith in government decreased
in all Americans (regardless of age or cohort) at
the time of the Watergate scandal.Age, cohort, and period effects are intertwined.
If one knows when an individual was born and also
knows the time of measurement, simple subtrac-
tion provides accurate information about the indi-
vidual’s age. Similarly, if one knows an individual’s
age and time of measurement, one can easily
calculate date of birth or birth cohort. Statistically,
there are no easy methods for disentangling age,
period, and cohort. In general, however, the most
compelling research results are those that are
based on examination of multiple cohorts at multi-
ple times of measurement. If the same age pat-
terns are observed across different cohorts meas-
ured at different times, those patterns are likely to
reflect age effects. If patterns are not similar across
cohorts and times of measurement, however, they
are likely to reflect cohort or period effects.The issue of age-period-cohort effects has lost
some of its appeal; critics point out that simply
knowing, for example, that there is a cohort effect
leaves unanswered what it is about those cohorts
that generated the observed differences. This is an
appropriate criticism; nonetheless, it is immensely
helpful in searching for causal explanations to
know whether the underlying mechanism is con-
sistent across time and place (an aging effect), had
strong contemporaneous effects on persons of all
ages (a period effect), or affected only specific
cohorts (a cohort effect). Age, cohort, and period
effects are all important in aging research. Age
effects provide information about human devel-
opment as it unfolds in social context. Cohort
effects permit us to observe the social implications